[PATCH v4 2/7] arm: clean up v7 and v8 linker scripts for bss_start/end

[Ilias Apalodimas]

commit 3ebd1cbc49f0 ("arm: make __bss_start and __bss_end__ compiler-generated")
and
commit f84a7b8f54db ("ARM: Fix __bss_start and __bss_end in linker scripts")
were moving the bss_start/end on c generated variables that were
injected in their own sections. The reason was that we needed relative
relocations for position independent code and linker bugs back then
prevented us from doing so [0].

However, the linker documentation pages states that symbols that are
defined within a section definition will create a relocatable type with
the value being a fixed offset from the base of a section [1].
So let's start cleaning this up starting with the bss_start and bss_end
variables. Convert them into symbols within the .bss section definition.

[0] binutils commit 6b3b0ab89663 ("Make linker assigned symbol dynamic only for shared object")
[1] https://sourceware.org/binutils/docs/ld/Expression-Section.html

Tested-by: Caleb Connolly <caleb.connolly at linaro.org> # Qualcomm sdm845
Tested-by: Sam Edwards <CFSworks at gmail.com> # Binary output identical
Signed-off-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
---
 arch/arm/cpu/armv8/u-boot-spl.lds        | 18 +++++++-----------
 arch/arm/cpu/armv8/u-boot.lds            | 16 ++++------------
 arch/arm/cpu/u-boot.lds                  | 22 +++++++---------------
 arch/arm/lib/sections.c                  |  2 --
 arch/arm/mach-rockchip/u-boot-tpl-v8.lds | 15 ++++-----------
 arch/arm/mach-zynq/u-boot.lds            | 22 +++++++---------------
 6 files changed, 29 insertions(+), 66 deletions(-)

diff --git a/arch/arm/cpu/armv8/u-boot-spl.lds b/arch/arm/cpu/armv8/u-boot-spl.lds
index 7cb9d731246d..8998c4985eac 100644
--- a/arch/arm/cpu/armv8/u-boot-spl.lds
+++ b/arch/arm/cpu/armv8/u-boot-spl.lds
@@ -63,18 +63,11 @@ SECTIONS
 
 	_image_binary_end = .;
 
-	.bss_start (NOLOAD) : {
-		. = ALIGN(8);
-		KEEP(*(.__bss_start));
-	} >.sdram
-
-	.bss (NOLOAD) : {
+	.bss : {
+		__bss_start = .;
 		*(.bss*)
-		 . = ALIGN(8);
-	} >.sdram
-
-	.bss_end (NOLOAD) : {
-		KEEP(*(.__bss_end));
+		. = ALIGN(8);
+		__bss_end = .;
 	} >.sdram
 
 	/DISCARD/ : { *(.rela*) }
@@ -89,3 +82,6 @@ SECTIONS
 #include "linux-kernel-image-header-vars.h"
 #endif
 }
+
+ASSERT(ADDR(.bss) % 8 == 0, \
+       ".bss must be 8-byte aligned");
diff --git a/arch/arm/cpu/armv8/u-boot.lds b/arch/arm/cpu/armv8/u-boot.lds
index fb6a30c922f7..9640cc7a04b8 100644
--- a/arch/arm/cpu/armv8/u-boot.lds
+++ b/arch/arm/cpu/armv8/u-boot.lds
@@ -149,19 +149,11 @@ SECTIONS
 
 	_end = .;
 
-	. = ALIGN(8);
-
-	.bss_start : {
-		KEEP(*(.__bss_start));
-	}
-
-	.bss : {
+	.bss ALIGN(8): {
+		__bss_start = .;
 		*(.bss*)
-		 . = ALIGN(8);
-	}
-
-	.bss_end : {
-		KEEP(*(.__bss_end));
+		. = ALIGN(8);
+		__bss_end = .;
 	}
 
 	/DISCARD/ : { *(.dynsym) }
diff --git a/arch/arm/cpu/u-boot.lds b/arch/arm/cpu/u-boot.lds
index 7724c9332c3b..0dfe5f633b16 100644
--- a/arch/arm/cpu/u-boot.lds
+++ b/arch/arm/cpu/u-boot.lds
@@ -207,23 +207,15 @@ SECTIONS
 	}
 
 /*
- * Compiler-generated __bss_start and __bss_end, see arch/arm/lib/bss.c
- * __bss_base and __bss_limit are for linker only (overlay ordering)
+ * These sections occupy the same memory, but their lifetimes do
+ * not overlap: U-Boot initializes .bss only after applying dynamic
+ * relocations and therefore after it doesn't need .rel.dyn any more.
  */
-
-	.bss_start __rel_dyn_start (OVERLAY) : {
-		KEEP(*(.__bss_start));
-		__bss_base = .;
-	}
-
-	.bss __bss_base (OVERLAY) : {
+	.bss ADDR(.rel.dyn) (OVERLAY): {
+		__bss_start = .;
 		*(.bss*)
-		 . = ALIGN(4);
-		 __bss_limit = .;
-	}
-
-	.bss_end __bss_limit (OVERLAY) : {
-		KEEP(*(.__bss_end));
+		. = ALIGN(4);
+		__bss_end = .;
 	}
 
 	.dynsym _image_binary_end : { *(.dynsym) }
diff --git a/arch/arm/lib/sections.c b/arch/arm/lib/sections.c
index 857879711c6a..8e8bd5797e16 100644
--- a/arch/arm/lib/sections.c
+++ b/arch/arm/lib/sections.c
@@ -19,8 +19,6 @@
  * aliasing warnings.
  */
 
-char __bss_start[0] __section(".__bss_start");
-char __bss_end[0] __section(".__bss_end");
 char __image_copy_start[0] __section(".__image_copy_start");
 char __image_copy_end[0] __section(".__image_copy_end");
 char __rel_dyn_start[0] __section(".__rel_dyn_start");
diff --git a/arch/arm/mach-rockchip/u-boot-tpl-v8.lds b/arch/arm/mach-rockchip/u-boot-tpl-v8.lds
index 74618eba591b..712c485d4d0b 100644
--- a/arch/arm/mach-rockchip/u-boot-tpl-v8.lds
+++ b/arch/arm/mach-rockchip/u-boot-tpl-v8.lds
@@ -56,18 +56,11 @@ SECTIONS
 
 	_image_binary_end = .;
 
-	.bss_start (NOLOAD) : {
-		. = ALIGN(8);
-		KEEP(*(.__bss_start));
-	}
-
-	.bss (NOLOAD) : {
+	.bss ALIGN(8) : {
+		__bss_start = .;
 		*(.bss*)
-		 . = ALIGN(8);
-	}
-
-	.bss_end (NOLOAD) : {
-		KEEP(*(.__bss_end));
+		. = ALIGN(8);
+		__bss_end = .;
 	}
 
 	/DISCARD/ : { *(.dynsym) }
diff --git a/arch/arm/mach-zynq/u-boot.lds b/arch/arm/mach-zynq/u-boot.lds
index 3b7c9d515f8b..3c5008b57392 100644
--- a/arch/arm/mach-zynq/u-boot.lds
+++ b/arch/arm/mach-zynq/u-boot.lds
@@ -103,23 +103,15 @@ SECTIONS
 	_image_binary_end = .;
 
 /*
- * Compiler-generated __bss_start and __bss_end, see arch/arm/lib/bss.c
- * __bss_base and __bss_limit are for linker only (overlay ordering)
+ * These sections occupy the same memory, but their lifetimes do
+ * not overlap: U-Boot initializes .bss only after applying dynamic
+ * relocations and therefore after it doesn't need .rel.dyn any more.
  */
-
-	.bss_start __rel_dyn_start (OVERLAY) : {
-		KEEP(*(.__bss_start));
-		__bss_base = .;
-	}
-
-	.bss __bss_base (OVERLAY) : {
+	.bss ADDR(.rel.dyn) (OVERLAY): {
+		__bss_start = .;
 		*(.bss*)
-		 . = ALIGN(8);
-		 __bss_limit = .;
-	}
-
-	.bss_end __bss_limit (OVERLAY) : {
-		KEEP(*(.__bss_end));
+		. = ALIGN(8);
+		__bss_end = .;
 	}
 
 	/*
-- 
2.37.2